The present invention relates generally to the field of circuit breakers, and more particularly to a molded case circuit breaker stationary line bus assembly.
In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
There are two modes by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position.
To engage the operating contacts of the circuit breaker, the circuit breaker operating handle is used to activate the operating mechanism such that the movable contact(s) engage the stationary contact(s). A motor coupled to the circuit breaker operating handle can also be used to engage or disengage the operating contacts. The motor can be remotely operated.
A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as 400 amps. To carry such current and the magnitudes of short circuit currents that such breakers will experience, the line terminal and stationary contact assembly are typically an integrated structure. As current flows from the line terminal through the stationary contact into the movable contact, magnetic forces are generated in the conductors, and in fact, in some instances the magnetic forces are relied upon to assist in separating the movable contact from the stationary contact and forcing the resulting electrical arc into the arc chamber of the circuit breaker. For higher current rated circuit breakers, the cross section of the contact and its corresponding conductors are increased to handle such higher currents.
It is well known to provide supporting structure for the stationary contact and its conductor to resist the magnetic forces experienced by the contact and its conductors. Such structures include a screw and metal combination supporting the stationary line conductor or utilizing a support post formed in the molded housing of the circuit breaker. These devices or techniques may result in loose parts or they do not provide sufficient shielding or assistance with respect to the magnetic forces generated in the line conductor and stationary contact. One solution to deflections experienced by the line conductors is the use of a lip molded into the circuit breaker casing as described in U.S. patent application Ser. No. 08/935,754 filed Sep. 23, 1997 and assigned to the assignee of this application.
However, there remains a need for a stationary line bus assembly that will attenuate adverse repulsive magnetic forces between the line conductors. There is also a need for a stationary line bus assembly that reduces the tendency of the electrical arc generated during contact separation to remain near the contacts as a result of the magnetic field generated by the contact conductors rather than moving into the arc chute. There is a further need to provide structural support for the stationary line bus during the closing operation of the circuit breaker.
The circuit breaker of the present invention includes the stationary line bus assembly. The stationary line bus assembly comprises a bus body supported by support legs with the bus body having a first longitudinal portion with a first end and a second end and a second longitudinal portion with a first end and a second end, with each second end portions of the first and second longitudinal portions terminating at a common end portion. The second longitudinal portion including a stationary contact bus and in a spaced relationship from the first longitudinal portion, wherein a space is defined between the first and second longitudinal portions. A line terminal is mounted on the first longitudinal portion and a contact is attached to the second longitudinal portion. In one embodiment, a bus support is attached to the bus body in the space between the first longitudinal portion and the second longitudinal portion and separated from the support legs of the bus body by an insulating barrier. The stationary bus support can have several configurations. The circuit breaker also includes a molded case including a main cover with a first terminal mounted in the case and having a stationary line bus assembly as well as a second terminal mounted in the case. A second contact is electrically coupled to the second terminal. An operating mechanism having an ON position, an OFF position and a TRIPPED position is coupled to the second contact. An intermediate latching mechanism is mounted in the housing and coupled to the operating mechanism. A trip unit coupled to the second contact and the second terminal with the trip unit and selective operative contact with the intermediate latching mechanism operates the circuit breaker under a short circuit condition or overload condition.
The present invention includes a method for making a stationary line bus assembly for a molded case circuit breaker.